The long-term goal of this continuing research is to understand the role of cytochrome P450 enzymes in developmental toxicity of environmental chemicals. Such effects are among the most significant concerns in environmental toxicology, and yet a mechanistic understanding is largely absent. Understanding these effects requires explicit knowledge of the CYP involved, given the central role of CYP in the oxidative biotransformation of xenobiotics and many regulatory molecules. At present, there is no animal model for which there is a synoptic view of developmental expression of the full complement of CYP genes. The dual goals of this research are to establish a comprehensive picture of normal and chemically impacted CYP gene expression during development, and to determine the roles of selected CYP in developmental toxicity of prominent environmental chemicals. The major effort will involve the zebrafish (Danio rerio) vertebrate model. The initial studies will establish the identities of zebrafish CYP in gene families 1-4 by profile Hidden Markov Models and Bayesian analysis. The expression of all CYP and induction or suppression by chemicals during development, will be determined by quantitative PCR and focused CYP gene microarrays. Expression of nuclear receptors potentially involved in CYP induction also will be examined. Key CYP induced during development will be examined for contribution to toxicity by interfering with their expression in chemically treated embryos. The roles of CYP 1 family genes (CYP1A, CYP1B1, and novel CYPlCs) in toxicity of o?t/jo-polychlorinated biphenyls will be established using receptor knockdown and CYP over-expression. The contribution of these CYP to oxidative stress, a possible common pathway to developmental toxicity, will be assessed. CYP regulated by the pregnane x receptor (PXR) will be similarly examined. The environmental relevance of findings in zebrafish will be tested by examining selected homologous genes in the fish species, Fundulus heteroclitus, from a Superfund site highly contaminated by PCBs. These studies will address further whether altered expression of CYP that are implicated in toxicity contributes to the resistance to PCB toxicity evolved in these fish. The studies will provide a uniquely comprehensive view of CYP in developing zebrafish, pointing to homologues that may be similarly involved in other vertebrate species. The studies will provide a lasting foundation essential to current and future assessment of the contribution of CYP to developmental toxicity of chemicals.